Transmission opportunity scheduling

ABSTRACT

Scheduling of transmission opportunities to prevent collisions is contemplated. The transmission opportunities may be scheduled for terminal units where transmissions of one terminal unit may collide or otherwise interfere with transmissions of another terminal unit. The transmission opportunities may be scheduled according to a time-frequency grid to prevent collisions in a time domain and/or a frequency domain.

TECHNICAL FIELD

The present invention relates to scheduling transmission opportunities,such as but not necessarily limited to scheduling transmissionopportunities for terminal units configured to facilitate wireless,wireline or optical signaling.

BACKGROUND

Some combination of wireless, wireline and/or optical signaling mediumsmay be used to facilitate transmissions between a plurality of terminalunits and an access point or other devices configured to facilitatefurther transmissions. In order to maximize throughput capabilities, itcan be beneficial to allow multiple terminal units to transmit at thesame time. The transmissions of one terminal unit may collide orotherwise interfere with transmissions of another terminal unittransmitting at the same time if the corresponding transmission is notproperly scheduled. The present invention relates to schedulingtransmission opportunities in order to prevent the transmissions of oneterminal unit from colliding with or otherwise interfering withtransmissions of another terminal unit scheduled for transmission at thesame time.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a communication system in accordance with onenon-limiting aspect of the present invention.

FIG. 2 illustrates a time-frequency grid in accordance with onenon-limiting aspect of the present invention.

FIG. 3 illustrates a flowchart for a method of scheduling transmissionopportunities in accordance with one non-limiting aspect of the presentinvention.

DETAILED DESCRIPTION

As required, detailed embodiments of the present invention are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely exemplary of the invention that may be embodied in variousand alternative forms. The figures are not necessarily to scale; somefeatures may be exaggerated or minimized to show details of particularcomponents. Therefore, specific structural and functional detailsdisclosed herein are not to be interpreted as limiting, but merely as arepresentative basis for teaching one skilled in the art to variouslyemploy the present invention.

FIG. 1 illustrates a communication system 10 in accordance with onenon-limiting aspect of the present invention. The communication system10 includes a plurality of terminal units 12 configured to transmit withan access point 14 over a common communication medium 16. The accesspoint 14 may be configured to communicate with the Internet or anothernetwork (not shown). The access point 14 may include a scheduler 18configured to facilitate scheduling transmission opportunities,intervals or other transmission parameters for the terminal units 12depending on its particular operating capabilities. The transmissionopportunities may be scheduled in accordance with the present inventionto prevent transmissions of one terminal unit 12 from colliding with orotherwise undesirably interfering with transmissions associated withanother one of the terminal units 12 configured to transmit over thecommon communication medium 16.

The terminal units 12 are illustrated for exemplary non-limitingpurposes to be cable modems 12 configured to facilitate transmissionswith an access point 14, which may be a cable modem termination system(CMTS) 14. The CMTS 14 and/or the cable modems 12 may be configured inaccordance with Data Over Cable Service Interface Specification (DOCSIS)1.1/2.0/3.0), the disclosures of which are hereby incorporated byreference in their entirety. FIG. 1 illustrates a cable modem A as alegacy DOCSIS 2.0 cable modem, a cable modem B as a legacy DOCSIS 3.0cable modem and cable modems C, D as DOCSIS 3.x cable modems. Thesedesignations are provided in order to illustrate some of the cablemodems 12 having disparate operating capabilities. In particular, thelegacy DOCSIS 2.0 configured cable modem A is contemplated to beconfigured to facilitate time domain multiple access (TDMA)transmissions at a single frequency bandwidth (e.g., 3.2 MHz), thelegacy DOCSIS 3.0 cable modem B is contemplated to be configured tofacilitate TDMA transmissions multiple frequencies and bandwidths (e.g.,3.2 MHz or 6.4 MHz), and the DOCSIS 3.x cable modems are contemplated tobe configured to facilitate frequency domain multiple access (FDMA),orthogonal frequency domain multiple access (OFDMA) and/or singlecarrier frequency domain multiple access (SC-FDMA) transmissions at anadjustable frequency bandwidth (e.g., 3.2 MHz-42 MHz, or more).

These particular operating characteristics of the cable modems 12 areprovided for non-limiting purposes in order to demonstrate thecapabilities of the present invention to schedule transmissionopportunities for terminal units 12 having disparate operatingcapabilities. The noted operating characteristics are particular tocable modems 12 configured to facilitate transmissions over a coaxialcable 16 or hybrid fiber optic (HFC) network, and are not intended tonecessarily limit the scope and contemplation of the present invention.The scheduler 18 contemplated by the present invention may be configuredto facilitate scheduling transmission opportunities for other types ofcommunication mediums 16, including those comprised partly or completelyof wireless, wireline or optical infrastructures. The scheduler 18contemplated by the present invention may also be configured tofacilitate scheduling transmission opportunities for other types ofterminal units 12, including terminal units configured as or included aspart of a mobile phone, a cellular phone, a computer, a gateway, etc.The scheduler 18 described herein adapts to the time domain andfrequency domain limitations of the illustrated cable modems 12 in orderto schedule transmission opportunities to avoid collision. The scheduler18 may be configured to leverage any other particular transmissionlimitation of the terminal units 12 to avoid collisions, which may varydepending on the type or operating capabilities of the terminal unit 12.

FIG. 2 illustrates a time-frequency grid 20 in accordance with onenon-limiting aspect of the present invention. The scheduler 18 may beconfigured to schedule transmission opportunities for the terminal units12 relative to the time-frequency grid 20. The time-frequency grid 20 isillustrated to define a time domain 24 and a frequency domain 26. Thetransmission opportunities are illustrated with cells, such as cell 38,that are rectangular shapes that comprise the time-frequency grid 20.Cells have both a time and frequency dimension. Cells 40, 42, and 44 areadjacent in time. Cells 44, 46 and 48 are adjacent in frequency. Eachtransmission opportunity may be defined relative to the time domain 24and the frequency domain 26 to specify a bandwidth and duration forsignals to be transmitted for particular one of the terminal units 12.

The scheduler 18 may be configured in accordance with the presentinvention to adjust the configuration of each transmission opportunityaccording to the particular operating characteristics of the terminalunit 12, such as to prevent transmission collisions. The time-frequencygrid 20 is also shown to be divided into four block times 30, 32, 34,36. Each block time corresponds with a particular interval of the timedomain during which transmissions, such as OFDM transmissions requiringfixed transmission intervals, are segmented Each block time 30, 32, 34,36 maybe comprised of a number of cells selectable by scheduler 18. TheOFDM transmission opportunities are shown to vary depending on thecorresponding block time 30, 32, 34, 36 in order to demonstrate theability of the scheduler 18 to vary transmission opportunities. Thescheduler 18 may be configured to maximize use of available bandwidthand/or to prioritize communications of one terminal unit over another.The scheduler 18 may also have other considerations in assigning cellsto particular terminals. For example, it may be desirable to preventoptical beat interference (OBI) in radio frequency over glass (RFoG)transmission systems, or to compensate for a particular terminal nothaving sufficient transmit power.

The cable modem 12 scheduled to transmit during each transmissionopportunity is identified with one of the alphanumeric characters A, B,C and D. The transmission opportunities may be scheduled depending on anamount of data requested by the cable modems 12 for transmission, apriority of one cable modem 12 over another cable modem, or some otherstrategy. The scheduling generally corresponds with identifying the oneor more cable modems 12 that are to communicate and the amount of dataneeded to be communicated. The scheduler 18 may be configured todetermine some or all this information and/or another device may providethe relevant information to the scheduler 18. The first block time 30 isscheduled to provide transmission opportunities for each of the cablemodems A, B, C, D, the second block time 32 is scheduled to providetransmission opportunities for the cable modems A and C, the third blocktime 34 is scheduled to provide transmission opportunities for the cablemodems B and D, and the fourth time block 36 is scheduled to providetransmission opportunities for the cable modems A and B. This exemplaryscheduling is presented to demonstrate some of the variability andcapabilities of the scheduler 18 and is not intended to necessarilylimit the scope and contemplation of the present invention.

The cable modem A is shown to be fixed to a particular bandwidth (e.g.,3.2 MHz) having a fixed width (W) in the frequency domain 26 due to thelimitations of its operating characteristics. This frequency limitationrequires the corresponding transmission opportunities to coincide withthe same portion of the frequency domain 26 (see block times 30, 32 and36 where transmission opportunities for cable modem A coincide with thesame bandwidth). A duration/length (L) in the time domain of thetransmission opportunities scheduled for the cable modem A during theblock times 30, 32 and 36 are shown to be adjusted according to anamount of data being transmitted, i.e., the duration one transmissionopportunity may be longer than another when more data is desired to betransmitted. The cable modem A may be characterized as having a fixedfrequency or frequency domain characteristic, or at least one that isnot dynamically changeable by the scheduler 18, and a variable durationor time domain characteristic. The scheduler 18 may adjust a length ofthe transmission opportunities assigned to the cable modem A accordingto amount of data requiring transmission or according to the factors(e.g., the need to prioritize another terminal unit) but the scheduler18 may be unable to rapidly change the frequency configurationassociated with the cable modem A (the fixed frequency may be adjustedbut the scheduler 18 may be prevented from making such adjustments on aburst-by-burst basis).

The cable modem B, unlike the cable modem A, is fixed to one of twopossible bandwidths (e.g., 3.2 MHz or 6.4 MHz), thereby allowing thecorresponding transmission opportunities scheduled in the four blocktimes to occupy either 3.2 or 6.4 MHz. As with the cable modem A, thescheduler 18 may be limited to adjusting only a duration/length of thetransmission opportunities assigned to the cable modem B to compensatefor data variability or other adjustment factors since the bandwidth isconstrained to one of the two bandwidths. Unlike the cable modem A, thescheduler 18 may schedule the cable modem B to transmit simultaneouslyat multiple center frequencies and multiple bandwidths (see block times34 and 36). The cable modem B is shown to be scheduled with twotransmission opportunities during the third block time 34, which may bebeneficial in allowing the cable modem B to transmit more data during aparticular block time 34 than it would otherwise be able to communicateif it were only assigned a single transmission interval during thatblock time 34. Optionally, one of the two transmission opportunitiesassigned to the cable modem B during the third block time 34 may overlapin the time domain relative to the other one of the two transmissionopportunities, which may result from data transmission requirementsnecessitating the two transmission opportunities.

The cable modem C and the cable modem D are shown to share atransmission opportunity during the first block time 30. The scheduler18 may schedule the cable modem C and the cable modem D to share thetransmission opportunity due to the ability of the cable modems C, D tomix subcarriers. The subcarriers assigned within the shared transmissionopportunity may be partitioned between the cable modem modems C, D,e.g., the cable modem C may be assigned to even subcarriers and thecable modem D may be assigned to odd subcarriers such that thesubcarriers used to transmit data for each of the cable modems C, D areinterlaced. The transmission opportunity for the second block time 32 isshown to be occupied entirely by the cable modem C, which may bedesirable if the cable modem C requests to transmit a large amount ofdata. The transmission opportunity for the third block time 34 is shownto be occupied entirely by the cable modem D, which may be desirable ifthe cable modem C no longer desires data transmission or the cable modemD has priority. The transmission opportunities assigned to the cablemodems C, D are shown to vary in the frequency domain for each of thefirst, second and third block times 30, 32, 34.

The cable modems C, D may have operating characteristics that allow themto be variable in the frequency domain 26 but fixed in the time domain24. The time domain restrictions on the cable modems C, D may be suchthat the scheduler 18 is forced to fix the corresponding transmissionopportunities in the time domain. The fixed time domain requirements ofthe cable modems C, D may limit the scheduler to make frequency domainadjustments in order to compensate for data transmission requirements,i.e., the bandwidth may be increased when more data is to be transmittedand decreased when less data is to be transmitted. The frequencydependent transmissions of the cable modems C, D may experience improvedperformance if a guard interval (GI) is included. The GI may bespecified by the terminal unit 14. The scheduler 18 may not necessarilyneed to be responsible for specifying GI but the scheduler 18 may beresponsible for adjusting the size of the schedule transmissionopportunities to make room for the GI.

The cable modems C, D may experience improved signal transmissioncapabilities if signals are transmitted as shaped pulses. The shapepulses may be beneficial in constraining the associated transmittedenergy in order to ameliorate leakage. If the signals during aparticular transmission opportunity assigned to one of the cable modemsC, D relates to an OFDM burst, such as one where the burst abruptlystarts and stops, a wave ramp or raised cosine window can be integratedto eliminate or ameliorating out-of-band leakage. The use of shapedpulses may be assigned by the scheduler 18 or a network administrator orother network controller responsible for managing transmission quality.The use of GI and/or shape pulses may be transparent to the schedulerand/or the cable modems C, D at least in that the additional dataassociated therewith may simply be hidden as part of the entire amountof data considered by the scheduler 18 as being requested fortransmission. In this manner, the scheduler 18 may not be required toprocess the GI or shape pulses other than to consider them as part ofthe data needing to be transmitted from the cable modems C, D.

FIG. 3 illustrates a flowchart 50 for a method of schedulingtransmission opportunities in accordance with one non-limiting aspect ofthe present invention. The method is described from the perspective ofthe scheduler 18 being configured to facilitate scheduling transmissionopportunities. The processes and other operations necessary tofacilitate implementation of the contemplated transmission opportunitiesscheduling may be facilitated with an application executing on thescheduler 18 and/or with other devices associated with a communicationsystem 10, including the access point 12 and/or terminal units 12associated with performing the desired transmissions. The scheduler mayinclude a non-transitory computer-readable medium comprisingcomputer-executable instructions stored therein for performing orcommanding the contemplated transmission opportunity scheduling. Themethod is described with respect to a system configuration whereterminal units desire transmission opportunities in order to facilitateupstream signaling through an access point configured to facilitatefurther upstream transmissions. The present invention is not necessarylimited to upstream communications and contemplates schedulingdownstream communications. The upstream communications are predominantlydescribed as upstream communications may be susceptible to collisionsand other inferences resulting from multiple terminal units attemptingto transmit upstream over a common communication medium.

Block 52 relates to the scheduler receiving or otherwise identifyingtransmission opportunity requests. The transmission opportunity requestmay relate to requests issued from the terminal units and/or the accesspoint to the scheduler in order to identify transmission opportunities.The scheduler may be configured depending on the particular networktransmission requirements to specify cells for desired transmissions.The scheduler may be configured to identify the necessity of GI or shapepulses or to otherwise analyze parameters associated with signaltransmissions when facilitating scheduling of the transmissionopportunities and/or the scheduler may be configured to facilitatescheduling without having to necessarily process certain transmissionrequirements. The scheduler may, alternatively, be configured to performthe scheduling without having to identify the data to be transmittedduring each block time, whether GI or she pulses should be used or othertransmission related parameters. Instead, the scheduler may be moresimply configured to identify the amount of data needed fortransmissions, the terminal units intended to transmit during each celland the transmission limitations of the terminal units so that thetransmission opportunities can be scheduled in a manner that maximizesthroughput and/or in a manner that achieves other desirable transmissioncharacteristics, i.e., prioritizing transmission of one device overanother instead of maximizing throughput.

Block 54 relates to the scheduler identifying the terminal unitsdesiring to transmit, i.e., the terminal units that should be scheduledto transmit during one or more of the available cells or otherspecifiable intervals comprising the time-frequency grid. The schedulermay identify the terminal units from the transmission opportunityrequests or based on a related request from a system administratortasked with processing terminal unit originating request fortransmissions. Once the terminal units scheduled for particular blocktime are identified, Block 56 relates to identifying frequency and/ortime domain constraints for the corresponding terminal units. Thefrequency domain constraints may be particular to terminal units thattransmit time domain symbols such that the corresponding terminal unitscan transmit signals within one or more fixed frequency bandwidths andwith a transmission duration/length that is variable, i.e., thetransmission duration is not required to approximately equal the blocktime. The time domain constraints may be particular to terminal unitsthat transmit frequency domain symbols such that the terminal units cantransmit signals at virtually any bandwidth but require a fixedduration/length for the corresponding transmissions, i.e., thetransmission duration approximately equal to the block time.

Block 58 relates to scheduling transmission opportunities for theterminal units identified for each block time. This may includeadjusting time domain and/or frequency domain variables depending on thecapabilities of each terminal unit. The particular configuration (sizeand shape) of the transmission opportunities for each terminal may varyfrom block time to block time depending on any number of factors. Thetransmission opportunities may be scheduled according to atime-frequency grid where each transmission opportunity is defined withtime domain and frequency domain parameters usable by the correspondingterminal unit to properly time their transmissions. Block 60 relates tothe scheduler publishing a schedule or otherwise instructing theterminal units of the scheduled transmission opportunities. Thescheduled transmission opportunities may be published for any number oftransmitting units and for any period of time, which may be partitionedor segmented into cells.

As supported above, one non-limiting aspect of the present inventioncontemplates the use of OFDMA upstream for a future version of DOCSIS.This invention proposes the use of TDMA to switch between PHY layers atthe CMTS to allow full usage of the available spectrum, or optionallywithout bonding the two PHYs together, in order to simplify deviceimplementation. When a new PHY is initially deployed, the presentinvention contemplates that much of the existing upstream will beconsumed with upstream carriers using the PHY for DOCSIS 2.0/3.0devices, leaving very little available spectrum in which to run the newPHY. To address this, the present invention contemplates “bonding” thenew PHY to the existing QAM carriers, so that all available spectrumcould be used. This, however, introduces a lot of additional complexity,particularly since the two PHY layers will likely be very different. Asan alternative, the present invention proposes to use TDMA to allow“switching” between the two PHYs at the CMTS, thereby allowing a new CMto operate only with the new PHY across all available spectrum, andavoiding the need for bonding these two PHYs together. This shouldimprove both the efficiency of the modems or other devices scheduled fortransmissions, as well as making them simpler.

It may be a cost/power savings if OFDMA devices do not need to bond OFDMtransmissions with legacy QAM signals, while allowing the best possibleusage of limited upstream spectrum. The present invention contemplatesthe use of “logical channels” in DOCSIS, where different devicestransmit with different modulations upstream at different times, toachieve a similar result. As alternative, the contemplated “switching”may be distinguished from “logical channels” at least in that the OFDM“channel” may span across multiple QAM signals. The present inventioncontemplates making OFDMA devices compatible with legacy DOCSIS deviceson upstream transmissions, without making the OFDMA devices “bond” thenew OFDMA PHY with legacy QAM carriers. This may include using TDMA(time domain multiple access) to switch between OFDMA (for new cablemodems), and QAM carries (legacy DOCSIS) for upstream bursttransmissions.

The OFDMA carriers contemplated for use in accordance with the presentinvention may need to conform to relatively fixed block times, typicallylong enough to accommodate a guard interval and a number of symbols thatare ideally two raided to an integer power, such as 4096 symbols. LegacyQAM carriers are more flexible on transmission time (specified inmini-slots), but must have fixed bandwidths, such as 6.4 or 3.2 MHz. Asshown above in FIG. 1, a new CMTS may include a blade for receivinglegacy ATDMA transmissions and another blade for receiving OFDMAtransmissions. (Only the upstream path is illustrated). Thus legacydevices A and B would transmit to the QAM blade and new OFDMA devices Cand D would transmit to the OFDMA blade; alternately, these could be twodifferent functions on the same blade with an internal split. The CMTSscheduler contemplated by the present invention may be configured togive each CM cells with a transmission times and frequencies thatprevents interference in either time or frequency. The appropriate bladewould receive either the QAM transmission or the OFDMA transmission.

FIG. 2 illustrates transmissions in time vs. frequency where OFDMAdevices may be assigned a block time. The QAM devices need frequencybandwidths, as illustrated as either 3.2 or 6.4 MHz. Thus in a firstOFDMA transmission block, devices C and D transmit OFDMA in a 20.8 MHzwide block using different subcarriers. Thus backwards compatibility ismaintained, latency is minimized, and bandwidth efficiency is held high.Note that the OFDMA transmission can use more powerful forward errorcorrection relative to legacy QAM. The full flexibility of OFDMAtransmissions can be employed to maximize throughput. For example,should a home have high attenuation, less OFDMA subcarriers can be usedto maintain required signal to noise ratios. In order to keep the CMTSscheduler as simple as possible, it may be necessary to use a simplerscheme whereby only QAM carriers are used during one block of time, andonly OFDMA is used during another block of time. In this case, there maybe some issues getting the QAM transmissions to end at the same periodof time. This can be alleviated either by using Continuous Concatenationand Fragmentation (for DOCSIS 3.0 devices) or simple fragmentation (fromDOCSIS 1.1/2.0), so as to avoid wasted bandwidth due to some spectrumbeing unavailable for use during a given time. The 5-42 MHz bandwidthmay be characterized as a contiguous block of OFDMA subcarriers, withspectral and temporal holes created for either QAM transmissions ordiscrete interferers.

While exemplary embodiments are described above, it is not intended thatthese embodiments describe all possible forms of the invention. Rather,the words used in the specification are words of description rather thanlimitation, and it is understood that various changes may be madewithout departing from the spirit and scope of the invention.Additionally, the features of various implementing embodiments may becombined to form further embodiments of the invention. In particular, inan optical implementation, the terminals 12 may transmit with differentwavelengths instead of different frequencies. Tunable lasers couldaccomplish changing wavelengths.

What is claimed is:
 1. A non-transitory computer-readable medium havinga plurality of non-transitory instructions operable with a cable modemtermination system (CMTS) configured to schedule transmission intervalsfor a plurality of cable modems, wherein at least a portion of cablemodems are time division multiple access (TDMA) cable modems and atleast a portion of the cable modems are frequency division multipleaccess (FDMA) cable modems, the TDMA cable modems and the FDMA cablemodems transmitting with the CMTS over a common communication medium,the non- transitory instructions sufficient to: schedule transmissionintervals for the TDMA cable modems and the FDMA cable modems totransmit with the CMTS over the common communication medium withoutinterference, interference occurs when transmission intervals associatedwith the TDMA cable modems interfere with transmission intervalsassociated with the FDMA cable modems.
 2. The non-transitorycomputer-readable medium of claim 1 further comprising non-transitoryinstructions sufficient to schedule the transmission intervals for afirst block time such that a first TDMA cable modem is scheduled tocommunicate within a first bandwidth for a first duration and a firstFDMA cable modem is scheduled to communicate within a second bandwidthfor a second duration, the first bandwidth being distinct from thesecond bandwidth to prevent bandwidth overlap.
 3. The non-transitorycomputer-readable medium of claim 2 further comprising non-transitoryinstructions sufficient to fix the second duration to approximate thefirst block time and to vary a width of the second bandwidth inproportion to an amount of data to be transmitted from the first FDMAcable modem such that the width of the second bandwidth is greater whenmore data is to be transmitted and smaller when less data is to betransmitted, thereby resulting in the second bandwidth being variabledepending on the amount of data to be transmitted by the first FDMAcable modem during the first block time.
 4. The non-transitorycomputer-readable medium of claim 3 further comprising non-transitoryinstructions sufficient to vary the width of the second bandwidth inproportion to available bandwidth such that the width of the secondbandwidth is greater when more bandwidth is available and smaller whenless bandwidth is available, the available bandwidth being determinedbased on bandwidth dedicated for use by other FDMA cable modems or TDMAcable modems scheduled to transmit during the first block time.
 5. Thenon-transitory computer-readable medium of claim 2 further comprisingnon-transitory instructions sufficient to schedule the transmissionintervals for a first block time such that a third FDMA cable modem isscheduled to communicate within the second bandwidth for the secondduration.
 6. The non-transitory computer-readable medium of claim 2further comprising non-transitory instructions sufficient to fix thefirst bandwidth and to vary a length of the first duration in proportionto an amount of data to be transmitted from the first TDMA cable modemsuch that the length of the first duration is greater when more data isto be transmitted and smaller when less data is to be transmitted,thereby resulting in the first duration being variable depending on theamount of data to be transmitted by the first TDMA cable modem duringthe first block time.
 7. The non-transitory computer-readable medium ofclaim 6 further comprising non-transitory instructions sufficient tovary the length of the first duration in proportion to a time length ofthe first block time such that the length of the first duration isgreater when more time length is available and smaller when less timelength is available, the available time length being determined based ontime dedicated for use by other TDMA cable modems scheduled to transmitat the first bandwidth during the first block time.
 8. Thenon-transitory computer-readable medium of claim 6 further comprisingnon-transitory instructions sufficient to select the first bandwidth tobe fixed to one of a plurality of available bandwidth depending onbandwidths dedicated for use by other TDMA cable modems and FDMA cablemodems scheduled to transmit during the first block time.
 9. Thenon-transitory computer-readable medium of claim 6 further comprisingnon-transitory instructions sufficient to schedule the first bandwidthto be one of 3.2 MHz and 6.4 MHz and the second bandwidth to be greaterthan the first bandwidth.
 10. The non-transitory computer-readablemedium of claim 9 further comprising non-transitory instructionssufficient to schedule the second bandwidth to equal a valuecorresponding with 42 MHz minus the first bandwidth.
 11. Thenon-transitory computer-readable medium of claim 1 further comprisingnon-transitory instructions sufficient to transmit schedulinginstructions to the FDMA cable modems and the TDMA cable modems, thescheduling instructions detailing transmission intervals and otherinformation needed by the FDMA Modems and the TDMA cable modems totransmit with the CMTS.
 12. The non-transitory computer-readable mediumof claim 1 further comprising non-transitory instructions sufficient tocharacterize each cable modem to be one of the TDMA cable modems and theFDMA cable modems according to identifying information transmittedtherefrom, the identifying information indicating whether thecorresponding cable modem requires one of a fixed bandwidth and a fixedduration, the cable modems requiring the fixed bandwidth beingcharacterized as TDMA cable modems and the cable modems requiring thefixed duration being characterized as FDMA cable modems.